Transmission of pictures by electricity



Nov. 9 1926.

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. J. w. HORTON ET AL TRANSMISSION OF PICTURES BY ELECTRICITY Filed May 19, 1924 u v 5 Sheets-Sheet 5 narratric current is Patented N... a, 1926.

JOSEPH W. HORTOH,,OF BLOOMFIELD, HERBERT E. IVES, OF MONTCLAIR, AND MAU- RICE 3. LONG, 01 GLEN RIDGE, NEW JERSEY, 'ASSIGNORB TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW" YORK, N. Y., A CORPORATION OF NEW YORK.

TRANSMISSION OI PICTURES BY ELECTRICITY.

Application filed ma 19, 1924; Serial a. 714,468.

This invention relates to the transmission,

of ictures by electricity, and moreparticulary to acommercially practicable system suitable for use in the ordinary telephone 5 plant. I

It was well known prior to this invention that pictures could be transmitted from one place and reproduced at another by the use of electricity. At the sending station, elecproduced having characteristics corresponding to the tone values of elemental areas of the pictures. These characteristics are transmitted to the reproducing station, where corresponding elemental areas 5 of a record blank are operated upon to 'reroduce the picture. Unless these characteristics are faithfully produced, transmitted,

' and utilized, the resulting picture is unsatisfactory.

Many attempts have previously been made I to produce physical equipment which would satisfactorily transmit pictures. So far as applicants are aware, none of these has resulted in a commercially practicable system.

Equipment hasbeen' devised to scan the picture to be transmitted in order to produce picture current having characteristics correspondin to the tone values of the elemental areas 0 the picture. Other apparatus has been produced-to amplify such current and to modulate a carrier wave therewith. At the reproducing terminal, equipment has been made to reproduce a picture from a modulated carrier wave. Systems have also been disclosed for rotating the sending and reproducing drums synchronously and for starting them simultaneously. I However, prior to this invention, this equipment had not been combined into a working whole suitable for the commercial transmission of pictures.

In a commercially practicable system, it is not only necessary to obtain faithfulness of reproduction. but such faithfulness must be obtained with a minimum of equipment which is' durable and easily manipulated. Preferably, each element in the system should be separately adjustable and have a linear characteristic withrespect to its function of passing on'the tone values of the picture. This linear relationship is essential to the greatest simplification of the operating technique. The important requirements of a commercially practicable system are a combination of relatively simple terminal elements purposely designed for use in an Another object is' to attain this result by.

the use of equipment which is adapted for use in the existlng telephone plant.

In one embodiment of the invention the picture characteristics are transmitted from a sending to a reproducing terminal station as modulations of a voice frequency carrier wave.

Revolvable, icture drums are used at both terminals. s the drums rotate, they are moved axially with respect to stationary sources of intense light, so that the elemental areas of the picture surface are helically scanned. The drums are driven by phonic wheels, which are maintained in synchronism-continuously by means of a synchronizing carrier wave of frequency lower than that-of the picture carrler wave, but still within the voice frequency range. The light at the sending terminal, passing through the transparency of the picture to be transmitted, variably energizes a photo-electric cell located within the sending drum, theintensity of energization corresponding to the tone values of the elemental areas as they are successively traversed. The resulting current from the photo-electric cell is amplified in a distortionless amplifier to modulate a voice frequency carrier wave in a modulator which is operated overthe distortionless portion of its characteristic. The char-' acter of the modulated current is such that it can be amplified, together with the synchronizin over a telephoneline or circuit for reproduction purposes at the re roducing terminal.

"A single string light va ve, actuated by the varying width. The picture drums are" carrier wave, in a telephone re-- peater without distortion for transmlsslon started simultaneously by the control of the scription having reference to the. accom panying drawing consisting of the following figures: I

Fig. 1 shows the method of arranging several of the succeeding figures of the drawing to illustrate a complete picture transmission system. Fig. 2 shows diagrammatically the scanning arrangement and drum driving equipment at the sending terminal of such a system.

Fig. 3 illustrates diagrammatically the modulating e uipment at the sending terminal for bot the picture and synchronizing carrier waves. I

Fig. 4 shows diagrammatically the sending terminal filters,. the sending terminal amplifier for raising the current level to a value suitable for impression upon a long distance telephone line and a test circuit for the picture modulator.

Fig. 5 shows diagrammatically part of the reproducing equipment including the picture carrier wave amplifier and synchronizing carrier wave amplifier and detector.

Fig. 6 illustrates the optical arrangement and drum driving equipment at the reproducing terminal.

Fig. 7 is an end view of the optical arrangement of Fig. 6.

Figs. 8 and 9 are fragmentary views showing details of the light valve greatly enlarged.

Fig. 10 illustrates a modification of the test circuit of Fig. 4.

Fig. 11 illustrates diagrammatically the arrangement of a source of illumination at the sending terminal.

Like reference characters are used in the several figures to represent like elements.

Detailed desm'iption.

v mounted on a shaft 7, which is carried by a carriage 8, whichslides on guides secured to a frame 9. The carriage 8 is moved along frame 9 b the rotation of shaft 10,

which is threadet for a portion of its length shaft 10 causes the rotation of shaft 7 through gear wheels 12 and 13. Gear wheel 13 is slidable along the shaft 10, but is forced to rotate therewith b means of a-ke sliding in a key-way. honic wheel 6 1s coupled to gear wheel 14 through pinion 15 and shaft 16, the latter being shown diagrammatically by dotted lines.v The gear wheel 14 is adapted to drive shaft 10 through a magnetically operated friction clutch. Gear wheel 14 is rotatably mounted on shaft 10. On either side of gear wheel 14 are friction members 17 and 18. Friction member 17 'is rigidly secured to shaft 10, while friction member 18 is slid-able therealon but forced to rotate therewith by a key sli mg in a key-way. The cncrgization of electromagnet 19 attracts an armature 011 clutch arm 20 to force the friction member 18 against gear wheel 14, and consequently gear wheel 14 against friction member 17. The action of clutch arm 20 on the friction member 18 is effected through ball bearing rollers 21, which engage friction member 18 at diametrically opposite oints. The clutch arm 20 is normally held in retracted position by a spring 22. Axial movement of the shaft 1.0 is prevented by collar 23 secured thereto.

The tuning fork SF is. driven by magnet 24 by current from a ower source (not shown) connected to switch 25. The driving magnet circuit is intermittently .interrupted at contact 26. Connected across con tact 26 is a spark killing circuit consisting of resistance 27 and condenser 28. The phonic wheel 6 is also driven by power from the source (not shown) through switch under the control of contacts 29 and 30. v

A resistance 31 is connected in series with the common conductor of phonic wheel 6. A spark killing circuit consisting of resistances 32 and 33, and condensers 34, 35, 36 and 37 are associated with contacts 29 and 30. Contact spring 38 carried by fork SF but insulated therefrom and contact 61 are connected through conductors 62 and 39 respectively, to the synchronizing carrier wave modulator of Fig. 3.

The energizing circuit for electromagnet 19 extends through main switch 40, control switch 41, stopping switches 42 and 43 and a holding switch on Fig. 3. When the switch 41 is closed to the left, stopping switch 42 is effective to oyien the energizing circuit of magnet 19; Whl e, with switch 41 closed to the right, stopping switch 43 is effective for this purpose.

In order to prevent interference from the the inside of the glass receptacle, which coating also covers a corrugated" metallic plate which serves as a terminal conductor. A glass extension 53 is provided to facilitate the forming of the cathode without having connection with the anode 51. A small clear glass window 54 is provided in the I cathode to allow the entrance of light from a source 55. An image of an aperture in the screen 56 which is intensely illuminated by light from source 55 is projected by means of lens 57 upon the surface of drum 5 to.

illuminate an elemental area thereof. The tone value of this elemental area determines the amount of light incident upon the oathode of the photoelectric cell 50. The arrangement of the aperture in screen 56 with respect to a helical filament 63 of source 55 is shown in Fig. 11. The width of the aperture is designated by distance 64. The screen may be located outside of the lamp bulb, but preferably it ismounte'd inside and as close to the filament as conditions warrant.

The cathode and anode of photo-electric cell 50 are connected to a picture amplifier PCA (Fig. 3) by conductors 58 and 59, respectively, both the photo-electric cell and the conductors being mounted Within a me tallic shield 60.

The picture current amplifier PCA consists of two electron discharge devices and 101, each having three electrodes. The filaments of devices 100 and 101 are heated from battery 102. The photo-electric cell 50 is connected to the input circuit of device 100 through a source of potential PEB and resistance 103. A negative polarizing battery 104 is used to give the grid a static negative potential. The source PEB 1s divided into three sections; 105, 106 and 107. Section 105 is made up of five batteries, the terminals of which are connected to the switch points of switch 108. Section 106 is made up of six batteries, the terminals of which are connected to the switch points of switch 109. Section 107 consists of a potentiometer 110 connected in series with battery 111 and resistance 112. Switches 108 and 109 are provided with double arms with resistance 113 connected therebetween so as to allow of connecting any number of available batteries in series without opening the main circuit or short .circuiting any of the batteries.

Connected in the output circuit of device IOO'is-a fbattery 114, resistance 115 and an ammeter 116. The input circuit of device 101 is connected to anintermediate of battery 114 at contact 117. The grid of device 101 is given a static biasing potential by means of potentiometer 118 connectoint ed across battery 119. In the output circuit of device 101 is connectedbattery 120, resistance 121 and ammeter 122.

Plcture current modulator PM consists of electron dischar e device 123 and its as'sociated input an output circuits. The grid ofmodula tor IMis given a static biasing potential by means of potentiometer 124 connected across battery 125 and resistance 126 in series. Switch 127, when thrown to the right, closes the potentiometer circuit at contact 128 and connects the input circuit of modulator PM to the output circuit of amplifier POA at contact 129. \Vhen the switch 127 is closed to the left, the circuit of potentiometer 124 is closed at contact 130 and a battery 131 is connected in series with the input circuit of modulator PM at contact 132. This latter circuit including battery 131 is provided for purposes of adjustment. The picturc'carrler wave oscillator circuit is connected to the input circuit of modulator PM at transformer 133, across the secondary of which is-connected resistance 134. Connected in the output circuit of modulator PM .is transformer 135,;ammeter 136 and battery 137.

Thepicture current amplifier PCA and the picture modulator PM, together with the photo-electric cell 50, are enclosed withinthe metallic shield 60. In order to prevent disturbances due to vibration, this shield, together with the photo-electric cell, amplifier, modulator and containing cab.- inet, are mounted on supports 138, 138 by means of sponged rubber pads 139, 139.

Picture carrier wzwe oscillator PO consists of electron discharge device 140 and its associated circuits. The filament is heated from battery 141, while plate current is supplied by battery 142 through choke coil 143. Resistance 144 and potentiometer 145 in series are connected in the output circuit. A feed back circuit is provided through rc-' sistance 146 and transformer 147. quency of the generator carrier wave is determined by condenser 148, which is connected across the primary of transformer 147. The static potential of the grid of device 140 is set by battery 149. Condenser 150 acts as a stopping condenser to prevent current from battery 142 from affecting .transformer 147.

The carrier wave from oscillator PO is controlled by switches 151 and 152. iVith switch 151 in its left hand position and switch 152 in normal position. current from the lower winding of transformer 153 is impressed upon the input circuit of modu- The frei circuit of modulator PM is then closedthrough potentiometer 155 at contact 156 of key 152 and contact 157 of key 151. With key 151 thrown in its right hand position, carrier current also from the lower winding of transformer 153 is impressed upon the input of the modulator PM through contact 154 of key 152, as previously explained, while the output cirouit of modulator PM is connected to the resistance 155 through contact 158 of key An independent circuit for the input carrier wave to modulator PM is provided through contact 159 of key 151. By means of keys 151 and 152, the entire secondary winding of transformer 153 may be connected directly to the resistance 155 by way of shield 60, contact 157 of ke 151 and contact 160 of key 152 indepen entl of the modulator PM. My means of switc 161, the output potentiometer 155 may be connected either to output conductors 162 and 163, as shown, or to a test circuit by way of conductors 164 and 165.

The synchronizing carrier wave is supplied by oscillator SO, which consists of electron discharge device 170 andits associated circuits. The filament of device 170 is' heated by current from battery 171. Plate current is supplied from battery 172 through choke coil 173. The generated wave is supplied to a modulator circuit 174 through resistance 175 and transformer 176. A feed back circuit is connected through resistance 177 to transformer 178. The frequency of the generated wave is set by condenser 179. The static grid potential is fixed by battery 180. A stopping condenser 181 is provided to prevent current from battery 172 from affecting transformer 178. The modulating circuit 174 consists of resistance 182 and potentiometer 183. Resistance may be omitted in some instances. The outputcarrier wave transmitted to conductors 184 and 185 is controlled by contact'61 and insulated spring 38 on tuning fork SF through conductors 39 and 62.

Spring 38 is insulated to prevent interference due to ground currents.-

Referring now to Fig. 4, sending icture filter SPF and synchronizing filter S F are provided to prevent interference between the picture apparatus and the synchronizing apparatus. Filter SPF is connected to the output circuit of the modulator PM by conductors 162 and 163; while filter SSF is connected to the potentiometer 183 by conductors 184 and 185. The other terminals of filters SPF and SSF are connected in parallel to conductors 200 and 201. The fil- SPF is a high pass filter consisting of three series condensers 202, 203 and 204, two inductive capacity shunts, consisting of condensers 205 and 206 and inductance coils 207, 208 and a third inductive shunt con,- sisting of inductance coil 209. The filter SSF is a band filter which consists of two series induct-ance coils 210 and 211, two series condensers 212 and 213, and a shunt condenser 214.

Conductors 200 and 201 are connected to the primary of transformer 215. The current level in conductors 201 and 202 is equivalent to the current level of an ordinary telephone transmitter, which is sometimes spoken of as zero level. In order to satisfactorily transmit this current over a telephone line, it must be suitably amplified. A two-stage electron discharge amplifier LA is provided for this purpose. The first stage of amplifier LA consists of electron discharge device 216 and its associated circuits. Between transformers 215 and 217, the secondary winding of the latter being connected to the input circuit of device 216, is an equalizer circuit and gain potentiometer 2.18. The equalizer circuit consists of resistance 219, condenser 220, inductance coil 221 connected in series between the. two halves of the secondary winding of transformer 215 and a shunt circuit connected across said winding consisting of a resistance 222 and a condenser 223. This equalizer attenuates the lower frequency currents more than the higher and so compensates for unequal attenuation of the transmission line. The resistance 222 and condenser 223 is omittedat the sending terminal.

when handling 135 cycle ringing current.

These elements consist of resistance 224, condensers 225 and 226, and relay 227 associated with the input circuit and condensers 228 and 229. and relay 230 associated with the output circuit. These elements have very little effect upon the amplifier when in a condition, as shown, to amplify voice frequency currents.

The second stage of amplifier LA consists of an electron discharge device 231 with its associated circuits. The filaments 216. flowing through choke coil 236, and thatfor device 231, through choke coil 243. The grid of device 231 is connected to potentiometer 237, one terminal of which is connected to the plate of device 216 throu h stopping condenser 238. The static gri potenof devices 216 and 231 are connected in se- .former 256. A static polarizing y tial for device 216 is supplied by battery 239 and that for device 231 by battery 240. The ampllrified output current of amplifier LA is pressed upon transmission circuit L through transformer 241, the wlich is connected in series wi The amplifier LA amplifies both the modulated picture carrier wave and the s n chronizlng carrier wave without distortion or intermodulation. Other amplifiers like LA are used as required.

The test circuit connected to conductors 164 and 165-consists of a variable artificial line 250, electron discharge amplifier 251 rimary of ta condenser and electron discharge detector 252. The 1 artificial line 250 is coupled to conductors. 164'and 165 by. means of shielded transformer 253. The input circuit of device 251 is coupled to the variable artificial line 250 by reslstance 254 and transformer 255. Thedevice 252 is coupled to device 251 b transpotential for device 251 is supplie battery 257; while one for device 252 is supplied by battery 258. The filaments of devices 251 and Y252 are heated by current from battery 259, while the plate current is supplied by battery 260. Rheostats 264 and 262 control the filament heating current of devices 251 and 252, respectively. The plate current of device 252 is indicated by an ammeter 261. In the modification of Fig. 10, the artificial line 250 is divided into two sections, a fixed section 262 and a variable section 263.- By means of switches 264, 264 the fixed section 262 may be removed from the circuit. The test circuit just described facilitates the-adjustment of the photo-electric cell battery PEB to insure a proper change in carrier wave amplitude between the dark and light conditions of photoelectric cell 50.

At the reproducing terminal (Fig. 5), the picture carrier wave and the synchronizing carrier wave are separated by filters RPF and RSF. Filter RPF is identical with filter SPF of Fig. 4 and filter RSF is identical with filter SSF of Fig. 4.

The received picture carrier wave from filter RPF is impressed upon the input circuit of electron discharge device 300 of receivingv picture amplifier RPA by potentiometer 301 i and transformer" 302. The amplifier carrier wave is either amplified or detected in receiving detector amplifier RDA, accordingly asit is required to operate the light va ve for picture reproduction or to start the rotation of the reproducing druna;

The reproducing detector amplifier RDA consists of an electron discharge device 303 and its associated circuits. The filaments of devices 300 and 303 areheated by current from battery 304.- Plate current for these devices is supplied by battery 305. The circui-t for device 300 includes choke coil 306.

' A- mie asssesame. grid of device 300 is *sup pfii through resistance 307.

For picture reproduction the reproducing v,

detector am lifier RDA functions as an amplifier'f wh1 e for starting the. picture drum 1t functions as a detector. The chan e over "is efiected by relays 308 and 309. en device 303 is fimctioning as an amplifier, the grid is olarized b battery 310, the circuit of whic is closed t rough contact 311 of re- 308 and includesthe upper portion only la of resistance 314. When function as. a detector, the grid is maintain at a larger negative otential by battery 312 the circuit of w ich is closed 'throu h contact 313 of relay 308 and includes t e whole of resistance- 314. denser 315 is provided to prevent. the grid of device 303' from being polarized. y battery 305. When the device 303 is functloning as an'amplifier', its output circuit is coupled to conductors 316 and 317 through transformer 318. The is connected to one terminal of the primary winding of transformer 318 by way of conductor 319, contact 320 of relay 308, and con ductor 321. The other terminal is connected to battery 305 by conductor 322.

If relay 308 is energized either b closure of switch 323 or the closure-0% contact 324 of relay 309, battery-312 is substituted for battery 310' by the closure of con-.

time the plate of device 303 is disconnected the' ed by the potentialdrop Stopping conlate of device'- 303 i from transformer 318 and connected to one terminal of relay 309 by the opening of contact 320 and the closure of contact 325 of relay 308. An'energi'zing circuit for relay 309 is thus completed from the plate ofpde-f vice 303 by way of conductor 319, contact 325 of relay 308,:conductor 326, ammeter J 330, winding'of relay 309 and conductor 322 to battery 305. If the icture carrier wave is incoming from the line L, detected current in the output circuit of reproducing detector amplifier RDA will energize relay 309 to maintain the energizing circuit of relay 308 at contact 324 (now closed) of relay 309. Condenser 327 is provided to improve the detecting action of device 303. A'shunt circuit about switch 323 and contact 324 con sisting of a condenser 328 and resistance 329, is provided to reduce sparking at these contacts. An ammeter 330 indicatesthe value of the detected current flowing in the relay The synchronizing carrierwave is amplitied in' reproducin RSA and detecte synchronizing amplifier in detector BSD. The

reproducing synchronizing amplifier BSA while the reproducing synchronizing detector RSD consists of electron discharge device 336 with its associated circuits. The filaments of devices 335 and 336 are heated by current from battery 337, the amplitude of which is determined b rheostats 338 and 339. Plate current for t ese devices is suplied by battery, 340. The input circuit on device 335 is coupled to the output of filter RSF by potentiometer 341 and-transformer 342. Device 336 is coupled to device 335 by transformer 343, connected in series with the secondary winding of which is a resistance 344 and a large negative polarizing battery 345. The static potential of the grid of device 335 is fixed by the potential drop in re sistance 346. A condenser 347 is provided to improve the detecting action of device 336. .Detected current from the output circuit of device 336 flows through ammeter 351 and conductors 348 and 349 to winding 400 of relay 401 of Fig. 6. Included in this out put circuit is the primary winding of a transformer 402, the secondary of which is connected in series with windlng 403. The induced current flowing in the secondary winding of transformer 402 aids in the positive operation of relay 401 when impulses of the synchronizing carrier wave are detected in the. synchronizing detector BSD.

Due to the intermittent receipt of impulses of synchronizing carrier wave, the armature of relay 401 vibrates between contacts 404 and 405. These contacts control the circuit of the driving magnet 406 of re-- ceiving tuning fork RF through a circuit which may be traced from the positive terminal of switch 407, conductor 408, winding of magnet 406, resistance 409, switch 410 .closed in its upper position switch 411,

closed in either its upper or lower positions, contacts 404 or 405 depending upon the position of switch 411, armature of relay 401, conductor 412, and conductor 413 to the negative terminal of switch 407 which is connected to ground.

The receiving tuning fork RF may also be driven independently of contacts 404 or 405 by closing switch 410 in its lower position so that the energizing circuit of magnet 406 extends through contact 414. A spark killing condenser resistance shunt consisting of condenser 415 and resistance 416 is connected around contact 404; while a similar shunt consisting of condenser 417 and resistance 418 is connected around contact 405. A phonic wheel 419 is driven by ower received through switch 407 under the control of contacts 420 and 421 of tuning fork RF. Connected in the common lead of phonic Wheel 419 is a resistance 422. A spark killing circuit consisting of condenser 423 and resistance 424 is connected around contact 420; while a similar circuit consisting of condenser 425 and resistance 426 is connected around contact 421.

The phonic wheel 419 drives a'reproducing drum 427 through the intermediary of shaft 428 shown diagrammatically b dotted lines. The mechanism for drivin ram 427 is identical with that shown an described in connection with Fig. 2 for driving sending drum- 5. It comprises shaft 428, carriage 429, gears 430 and 431, trance 432, car wheel 433 magnet arm 434, clutch mem .ers 435 and 436 and clutch magnet 437. The energizing winding of magnet 437 is under the control of switch 438 and stoppin switches 439 and 440. It is also controlle by switch 441 and contact 350 of relay 309. A spark reducing circuit consisting of resistance 462 and condenser 443 are connected in shunt of switch 441 and contact 350.

Amplified current from detector amplifier RDA. is impressed upon a single string light valve V by means of conductors 316 and 317. A single string 442 of the light valve V is suspended in an intense magnetic field of constant strength, maintained by current in winding 443. The string 442 normally closes an aperture between jaws 444 and 445. This aperture for convenience will be called the horizontal aperture. A vertical aperture is formed inscreen 446 (Fig. 7). The aperture forming members consisting of string 442, jaws 444 and 445, and screen 446 are intensely illuminated by light froma source 447 projected by lens 448. An image of the aperture is projected by lens 449 upon an elemental area of a light sensitive record blank mounted on receiving drum 427.

Details of the arrangement of the aperture forming members are shown in Figs. 8 and 9. These details are greatly enlarged. From Fig. 8 it is seen that the jaws 444 and 445 are mounted on string studs 450 and 451 respectively. The opening between the jaws 444 and 445 may be adjusted by screws 452 and 453 which pass through posts 454 and 455 respectively. These adjustments are exceedingly minute, since the total width of the string 442 is approximately 1/100 of an inch. A portion of the pole piece of the light valve V is shown with .a hole 456 through which the li ht from source 447 passes. Further detai s of the light valve and the method of reproducing the picture is described in a copending application of H.

'E. Ives, Serial No. 711,755, filed May 8,

picture current amplifier PCA. The moduated picture current together with synchro-.

ture carrier wave is selected from the line L by filter RPF, and amplified in amplifier EPA and reproducing detector amplifier RDA, functioning as an amplifier, the amplified current being used to operate the light valve V. The synchronizing carrier wave is selected by filter RSF and, after-amplification in amplifier BSA, is detected in detectorv RSD to drive the reproducing tuning fork RF through relay 401.

With key 151 Fig. 3 thrown to the left, the circuit of clutch magnet 19 is'opened at contact 184 and carrier current from the oscillator PO is transmitted to the modulator PM and thence to the line L through contact 154 of key 152 and contact 157 of key 151. By the closure of key 323 Fig.

' relay 308 is energizedto convert the reproducing detector amplifier RDA from an amplifier to a detector. The detected incoming carrier'wave then energizes relay 309 to maintain relay 308 energized independently of switch 323 by way of contact 324 (now closed). The energization of relay 309 opens the circuit of clutch magnet 437 at contact 350 regardless of the condition of the other contacts in the energizing circuit.

With the switch 151 in neutral position, contact 184 is closed, causing the energizetion of clutch magnet 19, providing the other contacts in the circuit are closed. The energization of clutch magnet 19 causes the rotation of drum 5 simultaneously with the energization of clutch magnet 19. The carrier wave from oscillator PO is disconnected from the modulator PM at contact 157. The interruption of the carrier Wave causes the deenergization of relay 309 at the reproducing terminal (Fig. 5). The deenergization of relay 309 closes contact 350' in the rier wave from oscillator PO is impressed upon the modulator PM by. Way of contact 159 and the output circuit of the modulator is connected to conductors 162 and 163 and thence by Way of amplifier LA to the line L by the closure of cont-act 158. Since the drum 5 is rotating,- this carrier wave is modulated by picture current corresponding to the tone values of elemental areas of the pic ture and istransmitted to the reproducing terminal and impressed upon the llght valve V to expose a record blank mounted on rotating drum 427. v

Method of operation.

The method of operation will now be described. I

The. picture drums 5 and 427 are set at .starting position in any suitable manner,

which in the ordinary case is their position at the completion of the transmitting process of the preceding picture. The transparency of the picture to be transmitted is placed on sending drum 5 and a light sensitive'record blank or film is, placed on. drum 427. Switch 40 is closed, key 151 is thrown to its left hand or hold position, whereby contact 184 is opened and 157 closes. Switch 41 is then closed in its right hand position. Au energizing circuit for clutch magnet 19 is thus prepared, the completion of which may be effected by the closure of contact 184 of key 151. At the reproducing terminal (Figs. 5 and 6) switch 441 is kept open to prevent the premature energization of clutch magnet- 437. Switch 438 is closed to the right. 011 the other hand switch 441 may be kept closed continuously and switch 438 maintained in its neutral or open position to prevent the premature energization of clutch mag-I net 437.

The circuits of the electron discharge devices may now be. energized. Synchronizing carrier waves from the oscillator SO are transmitted through modulator circuit 174, low pass filter SSF, amplifier LA, line L, low pass filter 'RSF, amplifier RSA to detector RSD. Picture carrier waves are supplied by oscillator PO to modulator PM by way of transformer 153, contact 154 of key 152, and transformer 133. This carrier wave is amplified in modulator PM and transmitted through high pass filter SPF, amplifier LA, line L, high pass filter RRF, amplifier EPA to detector amplifier RDA. Key 323 is closed long enough to energize relay 308 to cause the detector amplifierR-DA to function as a detector and to cause the energization of relay 309 by detected current from detector amplifier, RDA. The energization of relay 309 maintains the energization of relay 308 at contact 324 and opens the energizing circuit of clutch magnet 437 at contact 350. Switch 441 is then closed to complete the preparation of the energizing circuit for'clutch magnet 437, the completion of which is to be accomplished at contact 350 of relay 309.

Tuning fork SF is then set invibration and phonic wheel 6 started in such a direction as to move carriage 8 in the direction of the arrow upon the energization of clutch magnet 19. At contact 66 of forkSF potennisu'i with the vibration of the sending fork SF. The vibration of the armature of relay 401 causes impulses otcurrent in driving magnet 406 to drive" tuning fork RF in forced vibration in synchronism with the sending fork SF. Phonic wheel 419 is started in such a direction as -tocause the movement of carriage 429 in the direction of the arrow, when the clutch magnet 437 is energized.

Everything is now in readiness to start the transmission of the picture. Phonic wheels 6 and 419 are rotating synchronously. Drums 5 and 427 are stationary, due to the deenergized condition of clutch magnets 19 and 437 respectively. Relay 309 is energized by detected current from detector amplifier RDA.

' To start the actual transmission of the picture switch 151 is thrown to neutral position (as shown) in which condition contact 184 is closed and contacts 157, 158 and 159 are open. The closure of contact 184 completes the energizing circuit for clutch magnet 19 and starts the rotation and axial movement of drum 5. The opening of con tacts 157 interrupts the flow of carrier current to the reproducing terminal. The discontinuance or the receipt of the carrier wave by detector amplifier RDA permits the deenergization of relay 309 and consequently the deenergization of relay 308 by the opening of its energizing circuit atcontact 324 of relay 309. The deenergization of relay 308 converts the detector amplifier RDA The deenergization of relay 309 a so completes the energizing circuit for" clutch magnet437 at contact 350. The energization of clutch magnet 437 starts the rotation and axial movement of drum 427. The deenergization of relay 308 disconnects the output circuit of detector amplifier RDA from relay 309 and connects it to transformer--318 and thence to the string 442 of light'valve V The disconnection of relay 309 from the output circuit of detector amplifier RD'A at contact 325 of relay 308 prevents the further energization of relay 309 upon the subsequentreceipt of carrier current by the detectoramphfier RDA.

The var ing tone values of the successively scanne elemental areas of the transparency of the picture cause varyin current flow through the photo electric cel 50, and

icture amplifier POA. The carrier wave rom the oscillator PO is modulated by this varying current from amplifier PCA andafter amplification in amplifier LA, transmission over line L, amplification in amplifier EPA and detector amplifier RDA, function'ingas an amplifier, are im ressed upon thelight valve V to expose t e elementalareas of the light sensitive record blank mounted on drum 427 so as to reproduce the picture.

As the carriage 8 (Fig. 2) moves in the direction of the arrow, it encounters stopping switch 43 after the picture surface has been traversed and opens the energizing circuit of clutch magnet 19 at the contact of switch 43 to stop the picture drum 5. At the reproducing terminal (Fig. 6) the carriage 420 engages stopping switch 440 to open the energizing circuit of clutch magnet 437 at the contact of switch 440 to stop the reproducing drum 427.

The exposed record blank is now removed from the reproducing drum 427 and developed in ordinary manner.

. To transmit another picture phonic wheels 6 and 419 are reversed. Key 151 is thrown to its left hand position and key 323 is closed long enough to cause the energization of relay 309 by detected carrier current. A transparency of the picture to be transmitted is mounted on drum 5 and another light sensitive record blank or film is mounted on the reproducing drum 427. Switches 41 and 438 are thrown to the left. The circuit is now ready for the transmission of another picture and the process will be exactlythe same as hereinbefore .described except that-the carriages 8 and 429 will be moving in a direction opposite to that shown by the arrows and will be automatically stopped by stopping switches 42 and 439, instead of switches 43 and 440.

Preferred adjustment.

volt direct current source. The phonic wheel 6 is an impulse motor-capable of rotating at about 360 revolutions per minute. The forkSF is capable of adjustment within very close limits. The resistance 31 has a value of 50 ohms. Spark killing resistance 27 has a value of 200 ohms, while the condenser 28 has a capacity of 0.5 microfarad. Spark killing resistances 32 and 33 each have a value of 200 ohms, while the condensers 35 and 36 each have a capacity of 12 microfarads, Condensers 34 and 37 each have a capacity of 8 microfarads. The magnetic clutch which is actuated by ma et 19 is of the type disclosed in a copendi ng application of J. 0. Mesa, Serial No. 7 11,-

trated helical; filament.

752, filed May 8, 1.924. The, picture drum 5 is of the type disclosed in a copending ap- I approximately 3/16 of an inch, when-the screen is located outside the bulb, and 1/8 of an inch, when located inside. It is long enough to wholly expose the diameter of the helical filament. The image of the aperture is projected on the surface of the transparency of the picture by lens 57 as a rectangle 1/65 of an inchaxially of the drumand 1/130 of an inch tangentially. There are 65 threads to the inch on shaft 10 and the ratio of gear wheels 12 and 13 is unity, so that the picture surface is advanced 1/65 of an inch for each revolution of drum 5.

- The arrangement of the photo-electric cell 50, picture current amplifier PCA and modulator PM is similar to that disclosed in a copending application of D. M. Terry, Serial N 0. 711,749, filed May 8, 1924. The photo-electric cell is mounted within a metal tube or shield having a diameter of approximately 1 1/4 inches. -The section 105 of photo-electric cell battery PEB con sists of five units, each of 22.5 volts. Section 106 consists of sii: units, each of 4.5

volts.

Battery 111-consists of two units,

' each of 4.5 volts. Resistance 112 has a value 115 has a value of 100,000 ohms.

ometer 118 is similar to potentiometer 110. and has a total resistance 0f4,000 ohms arof 500 ohms, While the potentiometer 110 has a total resistance of 4000 ohms arranged in 40 steps. The resistance 103 consists of five units,-each having a resistance of 100,000 ohms. In the preferred arrangement, two units or a total of 200,000 ohms is employed. Battery 104 consists of one cell having a. potential of 1.5 volts. Battery total potential-of 135 volts, tap 117 being taken-off at a point Where the potential is 31.5 volts from the negative terminal. The left handportion of battery 114 consists of seven 22.5 volt units and three 4.5 volt units. The 31.5 .volt portion consists of one 22.5 volt units and two 4.5 volt units. Resistance Potentiranged in 40 steps. Battery 119 consists of one unit of 4.5 volts. Battery 120 has a po- 4,000 ohms arranged in 40 steps.

tential of 130.5 volts and consists of five- 22.5 volt units and four 4.5 volt units- Resistance 121 has a value of 100,000 ohms.

Pofentiometer 124 has a total resistance of Battery 125 consists of two--batteries each of 4.5

volts. Resistance 126 has .a value of,500

'a capacity of 0.0536 microfarads.

114 has a ing a resistance of 7 ohms. Battery 137 has a potential of 130 volts. Transformer'135 has an impedance ratio of 34,000 to 600 ohms, the low impedance-winding being coni nected to potentiometer 155, the total resistance of which is 600 ohms. Y

Going to the oscillator PO, transformer 147 has an impedance ratio of unity and each winding has an inductance ofv 380 millihenrys. Condenser 148 which has a capacity of 0.065 miorofarads, is connected across the' primary winding. Resistance 146 has av value of 100,000 ohms. Resistance 144 of 12,000 ohms is connected in series with potentiometer 145 of 800 ohms. 150 has a capacity of 2 microfarads. Choke coil 143 has an inductance of 62.5, henrys. The filament of electron discharge device 140 is heated by current from battery 141 of 6 volts, controlled by a rheostat having a resistance of 7 ohms. Plate current battery 142 has' a potential of 130 volts, while grid polarizing battery 149 has a potential of 9 volts. Transformer 153 has an impedance ratio of (300- to 600 ohnis. With the values just given for picture oscillator PO, the frequency of the generated carrier wave is approximately 1,000 cycles per second.

- Referringnow to synchronizing oscillator SO, the feed back coil 178 has an impedance ratio of unity, and each winding has an in- Condenser 179 has I Resistance 177 has a value of 400,000 ohms and resistance 175 has a value of. 12,000 ohms. Condenser 181 has acapacity of 2. microfarads. Choke coil 173 has an inductance of 62.5 henrys. discharge device 170 is heated by current from battery 171 of 6 volts under the control of a 7-ohm rheostat. Battery 172 has a potential of 130 volts. Transformer 176 ductance of 26 henrys.

has an impedance ratio of 1500 to 700 ohms,

the low impedance winding being connected directly to potentiometer 183 of 600 ohms, resistance 182 being omitted.

Filter SPF is a high pass filter adapted to freely transmit current of a range of frequencies-from 600 cycles per second and up. The condensers 202 to 206 inclusive have capacity values of 0.408, 0.312,- 0.331, 0.0497 and 1.456 microfarads respectively. Inductance coils 207 and 209 inclusive have inductance values of 320, 148, and 100 millihenrys respectively. Filter SSF is a narrowband filter adapted to transmit current of frequencies between 375 and 450 cycles, per second. ..I.nductance .coil.s 210.and. 211

Condenser The filament of electron Referring now to the ampli er LA, this isv substantially one half of a well known type 4-wire telephone repeater used in telephone systems. Transformer 215 has a one to one ratio. Resistance 219'has a value of 5000 ohms. Condenser 220 has a capacit of approximately 0.010 microfarads. In uctance coil 221 has an inductance of 0.4 henrys. Resistance 222 has a value of 3000 ohms; while condenser 223 has a capacity of 0.1 microfarads. Condenser 223 and resistance 222 are omitted at the sending terminal Potentiometer 218 has a resistance of 1540 ohms. By connecting a resistance of 1030 ohms in series and a resistance of 770 ohms in'parallel with potentiometer 218 an additional loss equivalent to 10 milesof standard cable may be introduced. Resistance 224. has a value of 1500 ohms. Condenser 225 has a' capacity of 0.075 microfarads and condenser 226, a capacity of 0.5 microfarads. Transformer 217 has an impedance ratio of 20,000 to 500,000 ohms, the high impedance Choke coil 237, has an inductance of 25 henrys.

winding being connected to the input circuit of the electron discharge device 216. Battery 239 has a potential of 1.5 volts. Choke coil 236 has an inductance of 350 henrys. Stopping condenser 238 has a capacity of one microfarad. Potentiometer 239 has a total resistance of 600,000 ohms made up of 12 resistance units, each having a resistance of 50,000 ohms. At least 150,000 ohms or three of the resistances should be included at all times in series with polarizing battery 240. Battery 240 has a potential of 9 volts.

Plate current for both devices 216 and 231 is supplied by battery 235, which has a potential of 130 volts. Filaments of devices 216 and 231 are connected in series with each other arid with a rheostat 233,

retard coil 234 having an inductance of-0.1 henrys, and battery 232 of 12 volts. Condenser 228 has a capacity of one-eighth micro- -farad; condenser 229, a capacity of one-half microfarad; and condenser 242, a capacity of one microfara'd. Transformer 241 has an impedance ratio of 6000 to 1540 ohms, the low impedance winding being connected to the line L. The mid-point of the low impedance windings of transformers 215 and 241 are each connected to ground.

The power output of the picture modulator PM and the synchronizing oscillator SC is approximately equivalent to the output of an ordinary telephone transmitter. Therefore, the current in conductors 200 and 201 is spoken of as being at zero level. The gain in amplifier-LA is variable up to 35 miles of standard cable and is adjusted, so as to raise the current level to a point suitable for transmission over a long distance telephone circuit. Between the amplifier LA and the re roducing equipment of Fig. 5, other ampli ers similar to amplifier LA are used depending upon the geographical separation of the terminal stations, and kind "of telephone circuit used. It may be neces- The re roducing filter RPF is identical with sen ing filter SPF. The reproducing synchronizing filter BSF is-identical with the sending synchronizing filter SSF. Filter RPF 1s terminated in a resistance 301 having a value of 600 ohms. The transformer 302 has an impedance ratio of 600 to 135,000 ohms, the high impedance winding being connected to the inputcircuit of electron discharge device 300. Resistance 307, the drop across which determines the polarizing potential of the grid of device 300, has a resistance of 1.6 ohms. Choke coil 306 has an inductance of 250 henrys. Condenser 315 has a capacity of two microfa-rads. The upper part of resistance 314 has a value of 6000 ohms, while the lower part has a value of 200,000 ohms. The filaments of devices 300 and 301 are heated by current ,from 6-volt battery 304. Battery 305 has a potential of 130 volts; battery 312, a potential about 35 volts; and battery 310, a potential 0159 volts. Transformer 318 has an impedance ratio of 6000 to 1.6 ohms, the low impedance winding being connected to the string 442 of light valve V. Condenser 327 has a capacity of one'tenth microfarad. The spark killing circuit connected in shunt of contact 324 of relay 309 consists of a condenser 328 having a capacity of one-tenth microfarad and a resistance 329 of 500 ohms.

The filter RSF is terminated in a potentiometer 341 of 600 ohms. Transformer 342 has an impedance ratio of 600 to 135,000 ohms, the high impedance winding being connected to amplifier RSA. Resistance 346 has a value of one ohm. Transformer 343 hasan impedance ratio of 20,000 to 500,000 ohms, the high impedance winding being connected in series with resistance 344 which has a value of one meg-ohm and battery 345 which has a potential of 35 volts. Filaments of devices 335 and 336 are heated by currentv from 6-volt battery 337 controlled by rheostats 338 and .339, each of 7 ohms re-' RSD. Condenser 347 has a capacity of 0.1

microfarad.

The string 4420f light valve V consists of a duralumin ribbon which is obtained by flat rolling a wire having a diameter of 0.003 of an inch (3 mils) down to a thickness of 0.00075 of an inch (0.75 mils). The width of this ribbon is approximately 0.01 of an inch (10 mils). It is suspended in a strong magnetic field-produced b winding 443. The ribbon vibrates laterally in the plane of its fiat surface, the length of the vibrating portion being approximately 1.25

inches. The coil 443 consists of 9,950 turns of No. 29 black enameled single silk insulated copper wire.

current source (not shown) to produce a flux density of approximately 35,000 gausses in the air gap between the pole faces. The tension of the string 442 is such that the natural period of its'vibrating portion is about 2000 cycles per second.

The horizontal a erture formed by jaws 444 and 445 is slig tly less'than the width of the string 442 or about 0.008 of an inch. The vertical aperture in the screen 446 is approximately 0.004 of an inch.

The drum-driving arrangement of Fig. 6 is substantially the same as that of Fig. 2. The light-sensitive record blank is mounted on drum 427 by the arrangement disclosed in'a copending application 'of'applicant Ives, Serial No. 711,042, filed May 5,

1924, Patent No. 1,545,897, granted July 14, 1925. The phonic wheel 419 and tuning fork RF are similar to the phonic wheel 6 and tuning fork SS at the sending terminal. The phonic wheel 419 and tuning fork RF, together with clutch magnet 437, are energized from a 110 volt direct current source connected to switch 407. Resistance 409 in series with driving magnet 406 has a value" of 1300 ohms. Resistance 422 in series with the common conductor of phonic wheel 419 has a resistance of 50ohms. Spark-killing resistances 424 and 426 eachhave a resistance of 10 ohms, .while condensers 423 and 425 each have a capacity of 12 microfarads. Spark-killing resistances 416 and 418 each have a value of 500 ohms, while condensers 415 and 417 each have a capacity of two microfarads. The spark-killing resistance 462 has a value of 500 ohms, and condenser 443, a capacity of one microfarad. v

Referring now to the test circuit of Fig. 4. transformer 253 has an impedance ratio of 600 to 600 ohms. Resistance 254 terminating in artificial line 250 also has a value of 600 ohms. Transformer 255 has an impedance ratio of 600 to 400,000 ohms, the

Current of 0.16 amperes. is supplied to the coil from a 110 volt direct ance ratio of 20,000 a. 500,000, ohms, the

high impedance winding bein connectedin series with battery 258 which as a potential of 30 volts. The filaments of devices- 251 and 252 are heated by current from'6-volt battery 259, the value of which is controlled by rheostats 264 and 262, eachof 7 ohms re'-' sistance. Ammeter 261 has a range of 0- to 15 milli-amperes. Plate battery 260 has a potential of 130 volts. The artificial line 250 is variable between zero and fifty miles of standard cable, i

In the modification of Fig. 10, the fixed artificial line 262 is preferably equivalent to 20 miles of standard cable. This value has been found to be satisfactory for newspaper reproduction. The artificial line 623 need not. therefore have as large a range as that of artificial line 250 or it may be replaced by a potentiometer. For the electron discharge devices of the operating embodiment under consideration, Western Electric Company vacuum tubes are employed having the following designations No. -101DW for devices 140,170, 231, 252, 303, and 336. No. 102DW for devices 100, 101. 123, 216, 251,300, and 335.

The sending terminal equipment is adjusted in the manner explained in a copending application of applicant Horton Serial No. 714,180, filed May 17, 1924. y The change in amplitude of output carrier wave corresponding to the change of light intensity within the photo-electric for a given picture is made equivalent to 20 attenuation units or 20 miles of standard cable.

In a system now in operation between Cleveland, Ohio, and New York city, the speed of the picture drums is such that the actual line time required for the transmission of a 5 x 7 inch picture is 4.6-minutes. At this rate eight pictures of this size each covering a different subject, have been transmitted in an'hour. The minimum time in which a 5 x 7 inch picture has been transas the record blank at the reproducing terminal, is 6.5 minutes. By increasing the speed of the picture drums the actual line time can be reduced to 1/3 or less of the value above given, so that a 5 x 7 inch picture {could probably be transmitted in one to one and one-half minutes.

In order to clearly disclose a commerciaL' 1y practicable embodiment of the inventioncertain design values and combinations of apparatus have been given hereinbefore. It

will be obvious to thoseskilled in the art that other values and combinations may be used to obtain satisfactory results. The equipment described, however, provides a transmission of pictures between distant places and functions properly with the existing telephone plant and uses only a single telephone circuit. This telephone circuit may consist of an ordinary telephone line, a phantom circuit, a carrier current telephone channel, or a radio telephone channel. The amount of equipment required is comparatively small, the technique of operating relatively simple, and the quality of the reproduction highly satisfactory.

In the system hereinbefore specifically described the reproduced picture is a posi tive of the'picture used at the sending terminal, that is, the light portions in the original appear as light portions in the reproduction. The equipment may be modified, so that the reproduction is a negative of the original. One convenient means of doing this is to insert another stage of amplification in 'the picture current amplifier PCA.

The desired proportionality of illumination of each elemental area of the recording sensitive surface may be obtained either by forming an image of constant brightness but varying size (Ives application Serial .No. 711,755 supra) or-Iby forming an image of constant size and variable intensity.

The scope of the invention is not to be limited to the specific embodiment hereinbefore described, but only by theappended claims.

"What is claimed is:

1. In a system for the transmission of pictures by electricity, a sending drum and a reproducing drum, means including voice frequency carrier current apparatus for rotating said drums in synchronism, a trans-- parency of a picture to be transmitted mounted on said sending drum, a light sensitive record blank mounted on said reproducing drum, a distortionless electron discharge amplifier for amplifying currents having frequencies from zero up to several hundred cycles, a photoelectric cell coupled to the input circuit of said amplifier, a source of current in the circuit of said cell, means to cause the excitation of said cell by passing light through elemental areas of said transparency, an electron discharge modulator resistance-coupled to the'output circuit of said amplifier to produce voice frequency carrier current modulated in accordance ith current from said amplifier, a single amplifier for amplifying both the modulated current and the synchronizing current, a telephone circuit for efficiently transmitting both the modulated current and the s nchronizing current, an amplifier for amplifying the modulated current received from said circuit, a light valve actuated by said amplified modulated current, an optical arrangement controlled by said light valve for reproducing the picture on said record blank, and a test circuit to facilitate the adjustment of the current in the circuit of said photoelectric cell. v

2. In a system for thetransmission of pictures by electricity, a sending drum and a reproducing drum, means including voice frequency carrier current apparatus for rotating said drums in synchronism, a transparency of a picture to be transmitted mounted on said sending drum, a light sensitive record blank mounted on said reproducing drum, a distortionless electron discharge amplifier for amplifying currents having frequencies from zero up to several hundred cycles, a PhOtOBlECtIIQ' cell coupled to the input circuit of said amplifier, a source of current in the circuit of said cell, means to. cause the excitation of sald cell by passing light through elemental areas of said transparency, an electron discharge modulatorvresistance-coupled to the output circuit of said amplifier to produce voice frequency carrier current modulatedin accordance with current from said amplifier, a single amplifier for amplifying both the modulated current'and the synchronizing current, a telephone circuit for efficient-ly transmitting both the modulated current and the synchronizing current, an amplifier for amplifying the modulated current'received from said circuit, a light valve actuated by said amplified modulated current, an optical arrangement controlled by said light valve for reproducing the pic ture on said record blank, and a test circuit including an artificial line to facilitate the adjustment of the currenti-n the circuit of said photoelectric cell.

3. In a system for the transmission of pictures by electricity, a sending drum and a reproducrngdrum, means including voice frequency carrier current apparatus for rotating said .drums in synchronism, a transparency of a picture to .be transmitted mounted on said sending drum, alight sensitii'erecord blank mounted on said repro- "ducing drum. a distortionless electron discharge amplifier for amplifying currents having frequencies from zero up to several hundred cycles, a photoelectric cell coupled to the input circuit of said amplifier, a

source of currentv in the circuit of said cell,

on said sending drum, a light sensitive rec- 0rd blank mounted on said receiving drum,

a resistancecoupled distortionless electron.

discharge amplifier for amplifying currents having frequency components from zero up to several hundred cycles, a photoelectric cell resistance-cou led to the in ut circuit of said amplifier an excited by 'ght passing through an elemental area of said transparency, an electron discharge modulator resistance-coupled to the output circuit of said amplifier to produce voice frequency carrier current distortionlessly modulated in accordance with current from said amplifier, a

' shield for said cell, amplifier and modulator,

a telephone circuit for efliciently transmitting both the modulated current and the synchronizing current, a distortionless amplifier for amplifying the modulated current received from said circuit, a light valve actuated by said'amplified modulated current, and an optical arrangement for exposing elemental areas of said record blank, the proportion of the area exposed being determined by the effect of said modulated current upon said light valve.

5. In a system for the transmission of pictures by electricity, at photoelectric cell energized by varying light intensities corresponding to the tone values of a icture, a distortionless amplifier for 'ampli ying current from said photoelectric cell, said current having frequency components from zero up to several hundred cycles per second, a n'iodulator for modulating a carrier Wave of audible frequency. by current from said amplifier, a shield for said cell, amplifier and modulator, a circuit for efiiciently transmitting said modulated wave having audible frequency components, means comprising ,a light valve controlled by the received modulated wave for reproducing a picture corresponding to the original, and a voicefrequency synchronizing arrangement forsynchronizing the energization of said photoelectric cell and said reproducing means.

6. In a system for the transmission of pietures by electricity, rotatable sending and reproducing drums, means including voice frequency carrier current apparatus for mounted on said sending drum, a'li ht sensitive record blank mounted on sai reproducing drum, an electron discharge amplifier for amplifying currents having frequencies from zero up to several hundred cycles, a" photoelectricrcell coupled to .the inputcircuit of said amplifier, a source of current in the circuit of saidrcell, means to cause the excitation of said cell by light passing through elemental areas of said transparency, an electron discharge modulator coupled to'the output circuit of said amplifier to produce'voice frequency carrier current modulated in accordance with current from re roducin drums means includin' voice frequency carrier current apparatus for maintaining said drums in synchronism, a transparency of a picture to be transmitted mounted on said sending drum, a light sen sitive record blank mounted on said reproducing drum, an electron discharge amplifier for amplifying currents having frequencies from zero up to several hundred cycles, a photoelectric cell coupled to the input circu1t of said amplifier, a source of current in the'circuit of said cell, means to cause the excitation of said cell by light passing through elemental areas of said transparency, an electron discharge modulator coupled to the output circuit of said amplifier to roduce voice frequency carrier current mo ula'ted in accordance with current from said amplifier, a single amplifier for amplifying both the modulated current and the synchronizing current, a telephone circuit for'transmit-ting both said currents, an electron discharge device for amplifying the modulated current received from said circuit, a light valve actuated by said amplified modulated current, an optical arrangement controlled by said light valve for reproducing the picture on said record blank, and means for converting said electron discharge device into a detector and for employing the detected current to control the starting of the sending. and reproducing drums.

8.-In a system for the transmission of pictures by electricity, rotatable sending and reproducing drums, means including voice 'voice frequency carrier current modulated in both said currents, an electron discharge de-' sitive record blank mounted on sai frequency barrier current apparatus for accordance with current from said amplifier, a single amplifier for am lifying both the modulated current and t e synchronizing current, atelephone circuit for transmitting vice for amplifying the modulated current received from said circuit, a light valve actuated by said amplified modulated current,

an optical arrangement controlled by said light valve for reproducing the picture on said record blank, and manual means for converting said electron discharge device from an-amplifier to a detector to cause the .starting of the sending and reproducing drums in unison.

9. A method for transmitting pictures over telephone lines, which comprises transmitting the picture characteristics as modulations of a carrier wave, the component frequencies of'which lie within a range exl tending from 600 to 2300 cycles per second,

transmitting a synchronizing carrier wave, the component frequencies of which lie Within a range extending from 350 to 450 cycles per second, and reproducing the picture .by

the optical effect of intermittent impulses of" light, said optical effect being controlled jointly by said modulated carrier wave and said synchronizing carrier wave. 10. A method for transmitting pictures over telephone lines, which comprises transmitting the picture characteristics as modulations of a carrier Wave, the component frequencies of which lie within a range'extending above 600 cycles per second, transmitting a synchronizing carrier Wave, the component frequencies of which lie within a range extending below 600- cycles per second, and rereducing the picture by the optical effect of intermittent impulses of light, said optical effect being controlled jointly by said modulated carrier wave and said synchronizing carrier wave. I

11. [nmethodfor transmitting pictures over telephone lines, which comprises transmitting the picture characteristics as modu lations of a carrier wave, the component frequencies of which lie within a range of audible frequencies above 600 cycles per second, transmitting a synchronizing carrier wave, the component frequencies of which lie within a range of audible frequencies below 600 cycles per second, and reproducin the picture by the optical effect of intermittent impulses of light, said optical efl'ect being controlled jointly by said modulated carrier wave and said synchronizing carrier wave.

12. In a picture transmission system, sending and receiving members, means including carrier current apparatus for rotatig said members in synchronism, a transpar ency of a picture to be transmitted mounted on said sending member, a light sensitive record blank mounted on said receiving member, an electron discharge amplifier for amplifying currents, a photoelectric cell coupled to the input circuit of said-amplier, a source of current in the circuit of said cell, means to cause the excitation of said cell by light passing through elemental areas of said transparency, an electron discharge modulator coupled to the output circuit of said amplifier to produce voice frequency carrier current modulated in accordance with current from said amplifier, a single amplifier for amplifying both the modulated current and the synchronizing current, a telephone circuit for transmitting both said currents, an amplifier for amplifying themodulated current received from said circuit, a light valve actuated by said amplified modulated current, an optical system con trolled by said light valve for reproducing the picture on said record'blank, a motor for forl; for controlling the-speed of said motor, a circuit for driving said fork, means at the receiving station for separating the synchronizing current from the modulated picture curren' t, and a relay repeatedly operated in response to said synchronizing current for opening and closing the circuit for driving said tuning fork.

In witness whereof, we hereunto subscribe our names this 19th day of May A; 1)., 1924.- I JOSEPH W. HORTON. HERBERT E, IVES. .MAURICE B. LONG.

driving said receiving member, a tuning 

